Field of the Invention
The present invention relates to a method of processing a single-crystal member such as a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, a gallium nitride (GaN) substrate, or the like.
Description of the Related Art
In an optical device fabrication process, an optical device layer made up of an n-type nitride semiconductor layer and a p-type nitride semiconductor layer is stacked on the surface of a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, or a gallium nitride (GaN) substrate, and optical devices such as light-emitting diodes, laser diodes, or the like are formed in a plurality of regions divided by a plurality of division lines formed in a grid pattern, thereby producing an optical device wafer. Then, a laser beam is applied to the optical device wafer along the division lines to cut the optical device wafer, dividing the regions with the optical devices formed therein thereby to manufacture individual optical devices.
As a method of dividing wafers such as the above optical device wafers, there has been tried a laser processing method that uses a pulsed laser beam having a wavelength permeable to the workpiece, wherein the pulsed laser beam is applied to the workpiece while positioning a converged point thereof within an area to be divided. A dividing process using such a laser processing method is a technology for dividing a wafer by applying a pulsed laser beam having a wavelength permeable to the wafer from one surface of the wafer while positioning a converged point of the laser beam within the wafer thereby to form a succession of modified layers serving as rupture start points along a division line within the wafer and applying an external force to the wafer along a street where the strength is lowered by the modified layers formed (see, for example, Japanese Patent No. 3408805).
Furthermore, as a method of dividing a wafer such as a semiconductor wafer, an optical device wafer, or the like along a division line, there has been put into practical use a technology for performing an ablation process on a wafer by irradiating the wafer with a pulsed laser beam having a wavelength absorbable by the wafer along a division line thereby to form laser-processed grooves, and applying an external force along the division line where the laser-processed grooves have been formed as rupture start points, thereby splitting the wafer (see, for example, Japanese Patent Laid-open No. 1998-305420).